Production of potassium polyphosphates from phosphate acid sludges

ABSTRACT

Phosphate acid sludges formed in the production of wet process phosphoric acids are converted to potassium polyphosphates by reaction with a potassium salt at elevated temperatures. Sodium salts may be introduced to reduce the fusion temperature and magnesium compounds with an increase in fusion temperature; the reaction system will also accept a variety of micronutrients. The potassium polyphosphate product formed has a high degree of citrate solubility establishing its excellent utility as a fertilizer.

United States Patent 1 Mills et al. v

[75] Inventors: Harold E. Mills; Michael B. Caesar,

both of Lake City, Fla.

[73] Assignee: Occidental Petroleum Corporation,

Los Angeles, Calif.

22 Filed: Sept. 10, 1971 211 Appl. No.: 17?,541

[52] US. Cl 71/1, 71/34, 71/46, 423/315 [51] int. Cl. C051) 7/00 [58] Field of search ..7l 4 -3 6 1, 46, 47, 25; 423/308, 312, 315

[56] References Cited UNITED STATES PATENTS 3,607,213 9/1971 Wrodaw et al 71/34 3,653,875 4/1972 Waters et a1 423/313 2,288,418 6/1942 Partridge 71/34 3,574,591 5/1971 Lyons et al. 1. 71/36 X 2,867,522 1/1959 Facer 71/47 X 3,291,594 12/1966 Nickers0n..... 71/47 X 3,455,649 7/1969 Bigot 71/34 Primary ExaminerSamih N. Zaharna Assistant Examiner-Richard Barnes Att0rney-Andrew .l. Belansky et al.

[57] ABSTRACT Phosphate acid sludges formed in the production of wet process phosphoric acids are converted to potassium polyphosphates by reaction with a potassium salt at elevated temperatures. Sodium salts may be introduced to reduce the fusion temperature and magnesium compounds with an increase in fusion temperature; the re-- action system will also accept a variety of micronutrients. The potassium polyphosphate product formed has a high degree of citrate solubility establishing its excellent utility as a fertilizer.

33 Claims, No Drawings BACKGROUND OF THE INVENTION The present invention relates to the formation of highly soluble potassium polyphosphate fertilizers from the phosphate acid sludges formed during the production of wet process phosphoric acids.

As part of the productionof wet process phosphoric acid there is an inevitable aging at the clarification stage in which insoluble, phosphate bearing precipitates are formed. The wet process phosphoric acids normally produced may range from merchant grade, namely an acid containing about 54 percent P to higher strength acids containing up to about 82 percent P 0 The nature of the precipitates will vary to some degree depending upon the strength of the acid produced. They will, however, be normally comprised of a liquid phase and a solid phase. The liquid phase of the sludge is phosphoric acid, while the solid phase contains, namely, undesirable orthophosphate salts.

In most cases, the liquid phase which has some value, is not separated from the solid phase and both are utilized in the manufacture of various solid forms of ammoniated phosphate fertilizers, such as diammonium phosphate (l8460) which provides a total plant food of about 64 percent with no polyphosphate content.

Depending upon the degree of difficulty in separating the acid from the solids, the phosphate acid sludge may account for up to 70 percent of the total P 0 with only 30 percent of the P 0 being present in the collected clarified acid.

Of the phosphate acid sludge, the solid phase may contain up to about 25 percent P 0 which is water insoluble and not completely available as a plant food.

Phosphate acid sludges have been mainly used for the production of diammonium phosphate and triple superphosphate. Both commodities, however, are in oversupply and of low profitability.

SUMMARY OF THE INVENTION It has now been found that phosphate acid sludge may be converted to a high nutrient value potassium polyphosphate byrea'cting the sludgeacid with a potassium salt, at temperatures of from about 750C to about l,l00C to form a homogeneous melt, then cooling the melt to form a solid in which all of the P 0 is available as a fertilizer, the polyphosphate content is high and depending upon the formulation, the product may be made to have slow release of properties. In addition, it may be made nonhygroscopic and therefore readily handleable for application in the dry form.

One method for producing potassium polyphosphates comprises'reacting phosphate acid sludge with a potassium salt-in which the mol ratio of potassium to phosphorous ranges from about 0.3 to about 2 by intimate mixing of the phosphate acid sludge with at least one potassium salt, then heating the resultant mixture 100C to about 150C to obtain the release of as much water as possible along with some chlorine, hydrogen chloride and fluoride prior to heating to a temperature at which the melt will form.

There may, in the practice of the process of this invention, be added sodium salts to reduce the temperature at which the melt will form as well as magnesium compounds and additional plant nutrients at some sacrifice in fusion temperature.

- The production of the potassium polyphosphates, in accordance with the present invention, are fully amenable to the addition of micronutrients, such as comto a temperature sufficient to form a homogeneous melt, driving off all the volatile components, then cooling and solidifying the formed potassium polyphosphate. Preferably the mixture is heated to a temperature from about 750C to about l,l00C.

In a preferred embodiment, the mixture is prereacted at moderate temperatures ranging from about pounds of manganese, molybdenum, boron, zinc, cobalt, copper, either in the single stage reaction or in the first state of the two stage reaction.

DESCRIPTION sidual phosphate bearing liquids remaining afte'r'the clarification stage. I

The process involves, in general, mixing the'phosphate acid sludge, both the liquid and solid phases thereof, with at least one potassium salt and heating the resultant mixture to a temperature sufficient to form a homogeneous melt, then cooling the melt to form the potassium polyphosphate.

This may be carried out in one stage or in two stages,

the latter involving a pre-heating to a temperature of from about C to about C to eliminate much of the water present in the reaction mixture prior to heating to an elevated temperature to form the homogeneous melt containing the potassium polyphosphate. This latter temperature will generally range from about 750C to about 1,100C.

The potassium salts which may be added to the phos phate acid sludge in accordance with the practice of the process of this new invention include among others, potassium chloride, potassium sulfate, potassium hydroxide, potassium carbonate, potassium sulfide, potassium polysulfide, and the like as well as mixtures thereof.

In formulating the mixture for the formation of potassium polyphosphates, the mol ratio of potassium to phosphorous should range from about 0.3 to about 2.0, preferably from about 0.5 to about 1.5.

There may also be added to the mixture a sodium salt which serves to reduce the temperature at which the melt is formed. The sodium salts which may be added include among others sodium chloride, sodium sulfate, sodium nitrate, sodium sulfide, sodium polysulfide and the like as well as mixture thereof.

Generally, the amount of sodium salt added is in an amount to provide a mol ratio of sodium to potassium ranging from about 0.2 to about 10, preferably from about 0.2 to about 0.4.

As indicated, the addition of the sodium salt to the system serves to reduce the fusion temperature or the temperature at which a homogeneous melt will form and otherwise serves only as a diluent.

There may be also added to the reaction system magnesium compounds as well as other micronutrients.

The magnesium compounds which may be added include among others, magnesium sulfate, magnesium oxide, magnesium chloride, magnesium orthophosphates and the like as well as mixtures thereof.

The addition of a magnesium compoundto the reaction system serves to control the hygroscopicity of the resultant product as a plant food supplement, particularly where the phosphate acid sludges are formed during the manufacture of superphosphoric acid which causesa depletion of magnesium from the phosphate acid sludge.

In general, when a magnesium compound is added, it is added in a mol ratio of magnesium to potassium of from about 0.2 to about 0.1 preferably from about 0.3 to about 0.5.

Micronutrients which may be added to the system in addition to magnesium include the salts of manganese, boron, molybdenum, zinc, cobalt, copper and the like as well as mixtures thereof. They are added, generally, in minor amounts, but it is most unexpected that the reaction systemwill accept these compounds. Generally, the micronutrients are added as salts but their inclusion in the oxide form is also feasible.

As indicated, the process of converting the phosphate acid sludges to potassium polyphosphates may be carried out in a single stage at a temperature ranging from about 750C to about 1,l00C depending upon the composition of the reactants. The actual temperature required can be readily determined in that reaction is complete when there is formed a homogeneous melt and all of the volatiles including hydrogen chloride, chlorine and fluorine, as well as water, have been evolved from the reaction system.

The melt, thus formed, is then cooled to form granular material or a solid mass which may be ground by conventional means such as hammer mills and the like into particles of a size suitable for use as a fertilizer.

Quenching or cooling the reaction mass may be by means of air or an inert liquid such as carbon tetrachloride. However, liquid quenching has not been found to have any material effect on the properties of the product.

Preferably, however, the process is carried out in stages. In the first stage, the reaction mixture is heated to a temperature from about 100C to about 1507C or more to remove at least a substantial amount of the water from the reaction mixture. There is also evolved at this temperature some of the chlorine, hydrogen chloride, and fluorides which may be separated from the melt mixture of reactants by any conventional means such as a venturi scrubber.

When the water content of the mixture is substantially eliminated the resultant mixture is then transferred to the high temperature zone where it is heated until the formation of the homogeneous melt occurs with attendant elimination of the balance of the volatiles.

The high temperature reaction may be carried out in any apparatus conventional to the formation of phosphate fertilizers, including among others, rotary kilns, reverberatory furnaces, fluid bed reactors and the like. Using such apparatus, the reaction may be carried out at subatmospheric, atmospheric or superatmospheric pressures.

In the process of this invention the amount of potassium added can have an effect upon the hygroscopicity of the product. Below a mol ratio of potassium to phosphorous of about 0.5 the product generally has the property of being non-hygroscopic. At the mol ratio of from about 0.5 to about 0.8 the product is mildly hygroscopic and above a mol ratio of about 0.8 the product has the property of strong hygroscopicity. As can be seen, hygroscopicity increases with the mol ratio.

The hygroscopicity of the product at any mol ratio, however, can also be modified by the addition of a magnesium compound which tends to reduce the hygroscopicity of the product making it less moisturesensitive and permitting ready distribution as a fertilizer in a dry form. The presence of a magnesium compound also adds valuable plant'nutrients to the product.

The particular advantages of the potassium polyphosphate manufactured in accordance with the practice of this invention, are that all the P 0 present is available as a fertilizer; polyphosphate content is high, ranging up to about 99 percent; and the product is high in total plant food content.

By varying the formulation, the product may be controlled to have slow release properties to permit its use as a long-term fertilizer. In addition, as indicated above, micronutrients can be readily and uniformly incorporated into the formulation.

While no wise limiting, the following are illustrative of the practice of the process of this invention. Unless otherwise indicated, all percentages are reported as weight percent.

In the examples, the following test methods or apparatus were employed during analysis of the feed or product:

1. P 0 Content, Wt. AOAC (*AOAC Association of Official Analytical Chemists, P.O. Box 540 Benjamin Franklin Station, Washington, DC. 20044) Method 12, pg. 13, llth Edition, 1970 2. P 0 Citrate Insoluble, Wt. %+AOAC Method 13,

pg. 14, llth Edition, 1970 3. P 0 1 hour water solubility, Wt. %+AOAC, pg,

14- 11th Edition, 1970" I 4. K 0 Water Soluble Content, Wt. %+AOAC, pg.

22 llth Edition, 1970; 2.0902.092

5. K 0 Total Content, Wt. Analyzed by Atomic Absorption Apparatus.

EXAMPLE 1 A quantity of superphosphoric acid solids was obtained by centrifuging freshly concentrated high strength wet process superphosphoric acid (83% P 0 in a basket centrifuge lined with teflon cloth. The acid temperature was approximately 180C. Water soluble P 0 remaining in the cake was removed by two successive hot water washes.

The residual sludge cake was removed from the centrifuge and oven dried. A typical analysis of the sludge solids was about 80% P 0 6% Fe O and 12% Al 0 with the P O in a highly insoluble form and not available as plant food.

One hundred seventy-three parts by weight of the sludge solids averaging 77.8% P 0 were dry mixed with 177 parts by weight potassium chloride, (61% K 0), and heated in a direct gas fired radiant roof furnace. The mixture quickly became molten and evolved hydrogen chloride and chlorine fumes which were re- Component Composition 150,1" 47.15% P 0.05% 130, 39.32% K O 35.75% Chlorine 0.21% pH (1% solution) 7.2 Moisture Absorption (24 hours at 75F, 75% RH) The formerly water insoluble P 0 was almost completely converted to available plant food. The product was low in residual chlorine, thus making it suitable for such crops as tobacco andpotatoes. The moisture absorption for this product was sufficiently low to-permit ready application to crops. Being water soluble, the product could also be used in the preparation of liquid or slurry fertilizers.

EXAMPLE 2 A sludge acid was obtained fromwet process phosphoric acid production and consisted of aqueous phos-,

phoric acid, its dissolved impurities, and solids precipitated during the concentration and clarification of the wet process phosphoric acid.

The liquid phase contains between 45% and 56% P 0 and the solid phase was a mixture of salts including gypsum, metal fluorides, metal phosphates, silicofluorides and complex salts such as ralstonite. Sludge acid was pumpable up to a solids content of about 25% by weight. The solids commonly contained from about 5% to of P 0, in an insoluble form.

Two hundred twenty-seven parts by weight of the sludge acid containing 48.9% P 0 and 10.4% solids were mixed with 82 parts by weight of potassium chloride (61% K 0) to form a paste. This mixture was heated with agitation to about 125C for about 1% hours to create a vortex to prevent spillage due to foaming. During this initial heating, steam and hydrogen chloride fumes were evolved and removed with a venturi scrubber system.

The hot semi-reacted material was then transferred to a gas fired furnace, brought to 840C and held at that temperature for about 1 hour. The melt formed was poured out as a thin layer onto a rotating heavy stainless steel plate, quenched and solidified. The product analyzed was as follows:

Component Composition P,o, 60.41% 1,O Not detectable 150 2.11% P,O, conversion to 99.30% non ortho form K 0 30.05% CaO 3.82% Chlorine 0.77% Moisture absorption (24 hrs. at 75F, 75% RH) 0.10% (165 hrs. at 75F, 75% RH) 1.70%

The P 0 content of the sludge acid was made completely available as plant food.

Compared with the product in Example 1, the product was found to be more slowly soluble in water and a slow release fertilizer. The hygroscopicity of this material was negligible.

EXAMPLE 3 i 4.77 parts by weight of dry solids precipitated from high strength wet process superphosphoric acid similar to that used in Example 1 and containing 78.5% of P 0 was dry mixed with 5.90 parts by weight fertilizer grade potassium chloride (61% K 0) and 1.35 parts by weight sodium chloride, to form a mixture having a mol ratio of K 0 to P 0 equal to 1.45, and a mol ratio of Na O to K 0 to 0.3. i

The mixture was heated in a vented muffle furnace for approximately 1 hour. Maximum steady furnace temperature during the fusion was 800C. As the mixture heated, it changed from solid to molten form, and bubbled with evolution of gases including water vapor, hydrogen chloride, phosphorous oxide vapor and iron chloride vapor,

1n the final molten state, at 800C, the melt was green in color, and poured easily onto a heavy stainless steel plate and there quenched and solidifed. The solid product analyzed was as follows:

Component Composition m 37.96% 150 0.11% P,O 8.70% K 0 34.87% Na,O 6.75% F o, 4.19% F1 0, (Water soluble) 2.15%

Substitution of part of the potassium content by sodium, appeared to increase-the water solubility, also reduce the temperature required to complete the fusion and created a low viscosity melt.

EXAMPLE 4 4.50 parts by weight of dry sludge acid solids precipitated from high strength wet process superphosphoric acid and containing 78.5% of P 0 was dry mixed with 5.15 parts by weight fertilizer grade potassium chloride (61% K 0) and 2.36 parts by weight of anhydrous magnesium sulfate to form a mixture having a mol ratio of K 0 to P 0 equal to 1.34 and a mol ratio of MgO to K 0 equal to 0.59.

The mixture was heated in a vented mufile furnace for approximately 1 hour. Maximumv steady furnace temperature duringthe fusion was 875C. As the mixture heated, it changed from solid to molten form, and bubbled with evolution of gases including water vapor, hydrogen chloride, phosphorous oxide vapor and iron chloride vapor.

1n the final molten state, at 875C, the melt was deepgreen in color and highly viscous. The melt was poured out onto a heavy stainless steel plate and then quenched and solidified. The solid product analyzed as follows:

Composition Substitution of part of the potassium by magnesium depressed water solubility.

EXAMPLE 5 A potassium polyphosphate containing agronomically desirable quantities of micronutrients was made as follows:

Part of sludge acid employed in Example 2, fertilizer grade potassium chloride (61% K and micronutrient containing salts were premixed in a tank in the quantities shown in Table 1.

The contents were transferred to a heated, agitated prereaction tank where they were held for about 1 hour at 100 125C. The slurry so formed was pumped continuously to an elevated weir flow controlling device which fed an equivalent to approximately 18 pounds per hour of the slurry to a high temperature reactor with any excess flow from the pump being returned to the pre-reaction tank.

The high temperature reactor was a direct gas fired countercurrent rotary kiln lined with a zircon ramming mix. Estimated retention time in the kiln was approximately 1 hour, and maximum pool temperature at the discharge end of the kiln was about 845C.

The melt was discharged continuously onto a water cooled stainless steel plate, thus forming a hard glassy form of potassium polyphosphate. This product was readily pulverized in a hammer mill to -10 +35 mesh, with less than of the material forming fines (-35 mesh). The product analyzed as follows:

Component Composition ,0; 49.87%

P 0 conversion to 93.10%

non ortho form Chlorine 0.14%

Moisture Abso tion (24hrs. at 75F, 75% RH) 10.10%

TABLE 1 Basic Formulation for Feed ingredient Parts Micronutrient Rate by Wgt. Parts by wgt./ Parts by wgt. P 0 Sludge Acid (46.3% P 0 10.0 Potash (61% K 0) 3.792 Borax (Na,B,O -10H,O) 0.408 Boron=1.0 Cobalt Nitrate [Co(NO ),61-l,O] 0.029 Cobalt-0.125 Cuprous Oxide (Cu O) 0.052 Copper=l .0 Potassium Permanganate 0.132 Manganese=l.0 (KMnO Molybdenum Oxide (M00 0.019 Molybdenum=0.25 Zinc Oxide (ZnO) 0.1 18 Zinc=2.0

EXAMPLES 6-1 0 Several studies were conducted in which sodiumpotassium molar ratios were varied from 0.20 to 0.40, in .05 mole increments. The levels of Na O added, represented 6 to 10% Na O in the final product. Analytical data from these tests shown in Table 2 indicated complete citrate solubility. Analysis for-K 0 was for water-soluble K 0 content. Total K 0 was not analyzed in these tests.

EXAMPLES 11 to 15 TABLE 2.EFFE(T OF SODIUM ON POTASSIUM POLYPHOSPHATE SOLUBlLlTY Citrate Ortho Mole ratio Total insol. W.S. Temp. P 0 P 0 P 0 K20 N020 F6203 Ex. Nai O/K:O K O/P O (C) (percent) (percent) (percent) (percent) (percent) F6203 (W.S.) Quench 6 0.20 1.45 800 37.96 0.11 8.70 34.87 6.75 4.19 2.15 Melt poured cold plate.

10 .40 1.45 800 38.62 .22 g 2.63 29.07 10.04 4.08 .55 Do.

TABLE 3.EFFECT OF MAGNESIUM ON POTASSIUM POLYPHOSP HATE SOLUBILITY Citrate Ortho I Total insol. W.S. Total W.S." W.S.

- Na Ol Temp. P205 P 0 P 0 K20 K 0 g Fe O;. Fg():|

Ex. K 0 K-=O/P O;, (C) (percent) (percent) (Percent) (percent) (percent) (percent) (percent) (percent) Quench 11.. 0.20 1.45 925 44.52 0 2.01 31.67 27.15 2.58 4.32 1.02 Melt poured 12.. .30 1.45 9.50 45.44 0 1.78 30.01 17.94 4.73 4.54 0.12 cold plate.

EXAMPLES 16 I 23 To investigate the effect of quenching on water solubility, of potassium polyphosphates formed from acid sludge a number of tests were conducted at 1( O/P O a K O/P O weightratio of 1:1, there appeared to be no material difference in product quality but that KC] had a more detrimental effect upon citrate solubility than potassium sulfate.

molar ratios of 1.2, 1.4, 1.6, and 1.8. One-half the melt 5 from each test was rapidly quenched by pouring the melt into cold CCl The other half was air-quenched EXAMPLE 28 by pouring onto a metal plate at ambient temperature. T determine the effect of secondary or trace ele- Data from thls serles are Shown m Table 10 ments on potassium polyphosphate solubility a'fusion No significant difference on product water-solubility mixture containing the following ratios by weight between rapid and slow quenching was determined. As' were evaluated. the K O/P O molar ratio was increased, the fusion temperature increased. The temperature spread from a 5 83 2 4 5 ""3 MR. of 1.2 and 1.8 was about 100C.

The temperatures required to effect fusion was about P EXAM LES 24 to 27 1,000C. Chem1calanalys1s at the feed m1xtures agreed The following tests were conducted to determine the closely with calcined values. The product was comeffect of using potassium sulfate as opposed to potaspletely soluble in ammonium citrate and yet contained sium chloride. Two tests were conducted at a K O/P O negligible water-soluble ortho phosphoric acid. The remolar ratio of 1.34 and two at a M.R. of 1.45. Below. sults are shown in Table 6.

TABLE 4 '24 hr. 24 hr Ortho total ortho Total c.|. w.s w.s. w.s. Total w.s.' T0131 w.s. Mole ratio Temp. P205, P205 P205 P205 P305 K20 K=O F620" Fe OK Quench Ex. Quench rate (KID/P205) ("C) (percent) (percent) (percent) (percent) (percent) (percent (percent (percent) (percent) media 1.2 800 46.83 0.17 9.53 46.13 12.33 36.03 34.09 (.1114 ('0... 1.2 47.21 .23 9.59 46.50 11.76 35.83 34.46 Air. 1.4 825 44.84 .11 9.25 44.15 10.18 36.29 c610 (:(1... 1.4 825 43.67 .24 9.89 43.32 10.41 38.04 Air. 1.6 850 40.08 3.88 7.95 35.71 8.25 37.67 35.84 3.92 3.25 (Sold C(Th. I6 850 41.95 2.51 8.19 38.13 9.25 36.82 35.29 ir. 1.8 900 38.92 2.42 13.51 34.83 13.56 41.20 37.82 3.95 3.21 (old C(h 1.8 900 39.84 2.17 2.58 38.06 13.25 40.01 37.85 Air.

.TABLE 5 Mole ratio Fusion Temp. Total P20; C.l. P20; W.S. P- O.-, w.s. K20 Ex. (K D/1 0;.) medium (C) (percent) (percent) (percent) (percent) 1.34 K2501 825 40.81 0 11.00 36.86 1.34 KCI 825 45.56 0 9.64 36.26 1.45 K2SO1 825 42.86 0 4.59 36.98 1.45 KCI 825 33.52 5.61 0.85 33.83

TABLE 6 Q1. w.s. 24 hr. Total P205 P205 ortho Total MnO ZnO M00 B20 Temp. P205 (p r- (P P205 K20 (per- (p r- (per- (per- Description (C) (percent) cent) cent) W.S. (percent) cent)" cent) cent) cent) MgO Feed mix 14 0/150 1.45 plus A as fusion media.... 27.05 25.78 0 0 25.39 0.53 2:07 0.60 0.44 3.92

Product...

.71110. 11.00... M110... Ni a 16o. 211.0.

What is claimed is:

1. A process for the production of potassium polyphosphate which comprises:

a. heating a mixture of at least one potassium salt and at least a phosphate acid sludge obtained in the clarification of wet process phosphoric acid in which the mole ratio of potassium to phosphorous is from about 0.3 to about 2.0 to a temperature sufficient to form a homogeneous melt comprising potassium polyphosphate formed by the reaction of the potassium salt and the phosphate acid sludge; and

b. solidifying said homogeneous melt.

2. A process as claimed in claim 1 in which the mixture of the potassium salt and phosphate acid sludge is heated to a temperature of from about 750C to about 1,100C.

3. A process as claimed in claim 1 in which the potassium salt is selected from the group consisting of potassium chloride, potassium sulfate, potassium hydroxide,. potassium carbonate, potassium sulfide and potassium polysulfide.

4. A process as claimed in claim 2 in which the potassium salt is selected from the group consisting of potassium chloride, potassium sulfate, potassium hydroxide, potassium carbonate, potassium sulfide and potassium polysulfide.

5. A process as claimed in claim 1 in which the mixture of the phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.

6. A process as claimed in claim 5 in which the mixture of phosphate acid sludge and the potassium salt is preheated to a temperature'of fiom about 100C to about 150C.

7. A process as claimed in claim 2 in which the mixture of the phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.

8. A process as claimed in claim 3 in which the mixture of phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.

9. A process as claimed in clairn 1 in which the mole ratio of potassium to phosphorous is from about 0.5 to about 1.5.

10. A process as claimed in claim 2 in which the mole ratio of potassium to phosphorous is from about 0.5. to about 1.5.

11. A process as claimed in claim 1 in which at least one sodium salt is added to the mixture of phosphate and sludge and potassium salt prior to reaction of mixture, the mole ratio of added sodium to potassium in the mixture being from about 0.2 to about 1.0.

12. A process as claimed in claim 11 in which the sodium salt is selected from the group consisting of sodium chloride, sodium sulfate, sodium nitrate, sodium V sulfide, and sodium polysulfide.

13. A process as claimed in claim 11 in which the mole ratio of sodium to potassium is from about 0.2 to about 0.4.

14. A process as claimed in claim 2 in which at least one sodium salt is added to the mixture of phosphate and sludge and potassium salt prior to reaction of mixture, the mole ratio of added sodium to potassium in the mixture being from about 0.2 to about 1.0.

15. A process as claimed in claim 14 in which the sodium salt is selected from the group consisting of sodium chloride, sodium sulfate, sodium nitrate, sodium sulfide and sodium polysulfide.

16. A process as claimed in claim 14 in which the mole ratio of sodium to potassium is from about 0.2 to about 0.4.

17. A process as claimed in claim 1 in which at least one magnesium salt is added to the mixture of phosphate and sludge and potassium salt prior to reacting the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.

18. A process as claimed in claim 17 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.

19. The process of claim 17 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 0.5.

20. A process as claimed in claim 2 in which at least one magnesium salt is added to the mixture of phos phate acid sludge and potassium salt prior to reacting the potassium salt and phosphate acid sludge the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.

21. A process as claimed'in claim 20 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.

22. The process of claim 20 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 23. A process as claimed in claim 11 in which at least one magnesium salt is added to the mixture of phosphate and sludge and potassium salt prior to reacting the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.

24. A process as claimed in claim 23 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.

25. The process of claim 23 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 0.5.

26. A process as claimed in claim 1 in which micronutrients are added to themixture prior to reaction.

27. A process as claimed in claim 26 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.

28. A process as claimed in claim 2 in which micronutrients are added to the mixture prior to reaction.

29. A process as claimed in claim 28, in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.

30. A process as claimed in claim 11 in which micronutrients are added to the mixture prior to reaction.

. 31. A process as claimed in claim 30 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.

32. A process as claimed in claim 17 in which micronutrients are added to the mixture prior to reaction.

33. A process as claimed in claim 32 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper. 

2. A process as claimed in claim 1 in which the mixture of the potassium salt and phosphate acid sludge is heated to a temperature of from about 750*C to about 1,100*C.
 3. A process as claimed in claim 1 in which the potassium salt is selected from the gRoup consisting of potassium chloride, potassium sulfate, potassium hydroxide, potassium carbonate, potassium sulfide and potassium polysulfide.
 4. A process as claimed in claim 2 in which the potassium salt is selected from the group consisting of potassium chloride, potassium sulfate, potassium hydroxide, potassium carbonate, potassium sulfide and potassium polysulfide.
 5. A process as claimed in claim 1 in which the mixture of the phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.
 6. A process as claimed in claim 5 in which the mixture of phosphate acid sludge and the potassium salt is preheated to a temperature of from about 100*C to about 150*C.
 7. A process as claimed in claim 2 in which the mixture of the phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.
 8. A process as claimed in claim 3 in which the mixture of phosphate acid sludge and the potassium salt is preheated to an intermediate temperature to remove at least a substantial amount of water from said mixture.
 9. A process as claimed in claim 1 in which the mole ratio of potassium to phosphorous is from about 0.5 to about 1.5.
 10. A process as claimed in claim 2 in which the mole ratio of potassium to phosphorous is from about 0.5 to about 1.5.
 11. A process as claimed in claim 1 in which at least one sodium salt is added to the mixture of phosphate and sludge and potassium salt prior to reaction of mixture, the mole ratio of added sodium to potassium in the mixture being from about 0.2 to about 1.0.
 12. A process as claimed in claim 11 in which the sodium salt is selected from the group consisting of sodium chloride, sodium sulfate, sodium nitrate, sodium sulfide, and sodium polysulfide.
 13. A process as claimed in claim 11 in which the mole ratio of sodium to potassium is from about 0.2 to about 0.4.
 14. A process as claimed in claim 2 in which at least one sodium salt is added to the mixture of phosphate and sludge and potassium salt prior to reaction of mixture, the mole ratio of added sodium to potassium in the mixture being from about 0.2 to about 1.0.
 15. A process as claimed in claim 14 in which the sodium salt is selected from the group consisting of sodium chloride, sodium sulfate, sodium nitrate, sodium sulfide and sodium polysulfide.
 16. A process as claimed in claim 14 in which the mole ratio of sodium to potassium is from about 0.2 to about 0.4.
 17. A process as claimed in claim 1 in which at least one magnesium salt is added to the mixture of phosphate and sludge and potassium salt prior to reacting the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.
 18. A process as claimed in claim 17 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.
 19. The process of claim 17 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 0.5.
 20. A process as claimed in claim 2 in which at least one magnesium salt is added to the mixture of phosphate acid sludge and potassium salt prior to reacting the potassium salt and phosphate acid sludge the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.
 21. A process as claimed in claim 20 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.
 22. The process of claim 20 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 0.5.
 23. A process as claimed in claim 11 in which at least one magnesium salt is added to the mixture of phosphate and sludge and potassium salt prioR to reacting the mole ratio of magnesium to potassium in the mixture being from about 0.2 to about 1.0.
 24. A process as claimed in claim 23 in which said magnesium salt is selected from the group consisting of magnesium sulfate, magnesium oxide-magnesium chloride, and magnesium ortho-phosphates.
 25. The process of claim 23 wherein the mole ratio of magnesium to potassium is from about 0.3 to about 0.5.
 26. A process as claimed in claim 1 in which micronutrients are added to the mixture prior to reaction.
 27. A process as claimed in claim 26 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.
 28. A process as claimed in claim 2 in which micronutrients are added to the mixture prior to reaction.
 29. A process as claimed in claim 28, in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.
 30. A process as claimed in claim 11 in which micronutrients are added to the mixture prior to reaction.
 31. A process as claimed in claim 30 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper.
 32. A process as claimed in claim 17 in which micronutrients are added to the mixture prior to reaction.
 33. A process as claimed in claim 32 in which the micronutrients are selected from the group consisting of salts of manganese, boron, molybdenum, zinc, cobalt and copper. 